Two-loop corrections to Bhabha scattering

The two-loop radiative photonic corrections to Bhabha scattering are computed in the leading order of the small electron mass expansion up to the nonlogarithmic term. After including the soft photon bremsstrahlung, we obtain the infrared-finite result for the differential cross section, which can directly be applied to a precise luminosity determination of the present and future e+ e- colliders.     

Radiactiv corrections to deeply virtual compton scattering

The non-commuting matrix elements of matrices from the quantum group GL _q(2;C) with q = being the n-th root of unity are given a representation as operators in Hilbert space with help of C ₄ ⁽ⁿ⁾ generalized Clifford algebra generators.The case of q C, |q| = 1 is treated parallelly.     

Two-loop QCD corrections to the longitudinal structure function

We calculate the fourth-order corrections to the longitudinal Wilson coefficient in deep inelastic scattering (for the non-singlet case). We use off-mass-shell states to control collinear singularities. A table of numerical results is presented for different numbers of quark flavours, and from these results we obtain the total next-to-leading order contributions to the moments of the longitudinal structure function.     

Two-loop corrections to the correlation function for tensor currents in gluodynamics

The results of evaluating the leading-order a_s corrections to the correlation function for tensor currents in pure gluodynamics are presented. These corrections to the parton result for the correlation function are not large numerically, which allows one to use perturbation theory to analyze the resonance spectrum within the sum-rule method.     

Second order logarithmic corrections to the Drell-Yan cross-section

We present a complete order α _s ² calculation of the large logarithmic terms of the type ln ⁱ (1?x)/(1?x) (x=Q ²/s), which appear in the Wilson coefficient of the total and differential DY cross-sections. These terms are computed using renormalizationgroup methods. It is shown that besides the well known constant part, they constitute the bulk of the radiative correction. This in particular holds for the higher τ-region which is still accessible to experiment. The large logarithmic corrections determine the shape of theK-factor and give a partial explanation of the phenomenon of anomalous scaling.     

Factorization for one-loop corrections in the Drell-Yan process

We study all the one-loop corrections to the Drell-Yan process in QCD, including gluon exchanges involving spectator partons. Our method demonstrates weak factorization at measured dimuon Q^T, and is suitable for generalization to higher orders.     

Two-loop QCD corrections to top quark width

We present O(α_s²) corrections to the decay t → bW in the limit of a very large top quark mass, m_t ⪢ m_W. We find that the O(α_s²) effects decrease the top quark decay width Γ_t by about 2%: Γ_t = Γ₀ (1 − 0.8α_t (m_t) − 1.7α_s²). The complete corrections are smaller by about 24% than their estimate based on the BLM effects O(α_s²). We explain how to compute a new type of diagrams which contribute to Γ(t → bW) at the O(α_s²) level.     

Large perturbative corrections to the Drell-Yan process in QCD

The total cross section $\text{d}\text{σ}\text{d}\text{Q}{}^2$ for the production of a muon pair of invariant mass Q²via the Drell-Yan mechanism and the Feynman x_F differential cross section $\text{d}{}^2\text{σ}\text{d}\text{Q}{}^2\text{d}\text{x}{}_{\mathrm{<mtext>F</mtext>}}$ are calculated in QCD retaining all terms up to order α_s(Q². The calculations are performed using dimensional regularisation of the intermediary infrared and collinear singularities, but we present our results in a form independent of such details. The corrections to both these cross sections coming from radiative corrections to the lowest-order $\text{q}\text{q}$ annihilation diagram are found to be large at present values of Q² and S when the cross section is expressed in terms of parton densities derived from leptonproduction, for all Drell-Yan processes of practical interest. Numerical calculations are presented which show, for any reasonable parametrisation of the parton densities, that the neglect of higher-order terms in α_s(Q²) is not justifiable. The quark-gluon diagrams on the other hand give small corrections in this order and are only important for PP scattering.     

Total calculation of electroweak corrections to the Drell-Yan process for LHC

A complete calculation of $ \mathcal{O} A complete calculation of (α) electroweak radiative corrections to the Drell-Yan process for future experiments at the Large Hadron Collider (LHC) is performed. All contributions to cross sections and kinematical constraints are presented; in calculations and in order to simplify programming, the formalism of theta and delta functions is extensively used in numerical estimations. The independence of the results from unphysical parameters is tested, the independence from the parameter separating the regions of soft and hard photons being proven analytically. A numerical analysis of hypothesized effects is performed by means of the READY code in the FORTRAN language with allowance for experimental constraints at the Compact Muon Solenoid (CMS) detector. The electroweak corrections in question prove to be significant in the region of large dilepton invariant masses M, reducing substantially the differential cross section with respect to M and forward-backward asymmetry. Original Russian Text ? V.A. Zykunov, 2008, published in Yadernaya Fizika, 2008, Vol. 71, No. 4, pp. 757–770.     

Radiative corrections to the helicity asymmetries for the Drell-Yan process in QCD

The next-to-leading-logarthmic corrections to the helicity cross sections for the Drell-Yan process are calculated. While it is well-known that these corrections are large, it is shown here that when considering the helicity asymmetry (initial-initial) these large radiative effects cancel. Thus the leading-order calculation for the asymmetry is a good approximation.     

Two-loop SUSY QCD corrections to the chargino masses in the MSSM

We have calculated the two-loop strong interaction corrections to the chargino pole masses in the scheme in the minimal supersymmetric standard model with complex parameters. We have performed a detailed numerical analysis for a particular point in the parameter space and found corrections of a few tenths of a percent. We provide a computer program that calculates chargino and neutralino masses with complex parameters up to .     

NLO QCD corrections to Drell-Yan processes in the SANC framework

NLO QCD corrections to charged and neutral current Drell-Yan processes are computed with help of the computer system SANC. At the partonic level both quark-antiquark and quark-gluon scattering channels are taken into account. Subtraction of collinear singularities in the massive quark scheme is compared with the one in the $ \overline {MS} $ \overline {MS} scheme. Numerical results at the hadronic level are received for the LHC conditions with help of Monte-Carlo integrators and event generator programs based on the standard SANC modules. Comparison with analogous results of the MCFM package is shown.     

QCD corrections to the Drell-Yan mechanism and the pion structure function

We compute the differential cross section dσ/dQ² dy for lepton pair production up to first order in the strong coupling constant α_s. We show that, in the region where the theory applies and where the statistical accuracy of the experiments is good, the ratio of the QCD correction to the Drell-Yan cross section is approximately constant, and that its magnitude is in good agreement with the results of the CERN-NA3 experiment. We thus show that, within the framework of this first-order calculation, the shape of the pion structure function extracted from dilepton production in πp collisions is approximately correct. We also comment on the average transverse momentum of the dilepton due to gluon or quark recoil.     

Radiative corrections to the Drell-Yan process at large dilepton invariant masses

Electroweak radiative corrections to the neutral-current Drell-Yan process at large dilepton invariant masses are calculated. Asymptotic expressions are obtained for diagrams involving two-boson exchange, which represent one of the most significant contributions to the reaction being studied. The contributions of vertex diagrams and “soft” bremsstrahlung are also taken into account. A numerical analysis of electroweak effects with allowance for experimental constraints at the CMS facility is given. The result obtained from this analysis makes it possible to ensure a high precision in the region of high energies; therefore, it is applicable to future experiments at LHC.